Heretofore, treadmills have been designed with either an exercising platform having an inclined tread surface or a horizontal tread surface upon which a person walks or runs in place. While such treadmills provide users with a good overall workout, they limit the accuracy of cardiac and aerobic tests and poorly simulate actual walking or running conditions. Furthermore, a treadmill with an inclined grade can often overstress certain of the leg muscles and understress various other leg muscles. In order to alleviate the problems, some treadmills have been designed so that the grade of their exercising platforms can be continually adjusted from a level position to a position with an inclined grade in order that actual walking or running conditions may be better simulated, but none of these known prior art machines provides a successful adjustment feature for the tread surface that simulates conditions of walking or running downhill.
Furthermore, many people consider traditional treadmills to be an unexciting, tedious, and even boring way to exercise. Consequently, treadmills with a variety of features have been introduced in order to make exercising more interesting, such as treadmills with an added television monitor, added headphone set, and/or a heart monitoring meter. However, these features are simply add-on features to the basic treadmill and still give the user the tiring and sometimes monotonous feeling that he or she is still simply walking or running on a treadmill. Even treadmills with computerized exercise programs for automatically varying the grade and speed of the exercising platform have only a limited ability to overcome the inherent monotony of the treadmill, and the exercising platforms of these treadmills usually can only be positioned with their tread surfaces in a horizontal or in an upwardly inclined position.